In general, a plurality of switches on a path determine the path from a sending source of a packet to a sending destination of the packet, and process packet-transfer. But, as an information processing system becomes diversified and scaled up, it is necessary to determine the path, which matches quickly with a change in a network configuration, adequately and flexibly. Then, as an art that, in a computer network, an external controller carries out one-dimensional control for a transfer operation of each switch, OpenFlow (OF) has been proposed (for example, refer to Japanese Patent Laid-open No. 2011-166384).
According to OpenFlow, an OpenFlow Switch (OFS) carries out an operation, which is set in Action, to a packet including Match Field which matches with a condition. Match Field has composition using a network hierarchy including Layer 1 (L1) to Layer 4 (L4). When receiving an unknown Match Field (unknown packet), OFS sends the packet to OpenFlow Controller (OFC) through OF-Ch (OpenFlow Channel). OFC outputs a flow to an adequate OFS on the basis of a packet destination. Then, OFC registers the flow with a flow table of each OFS by using the flow-mod message. Once the flow is registered, with reference to the registered flow table, OFS carries out communication related to a flow which is inputted into Ingress (entrance switch) at a next time or consequent times and which matches with a condition of the flow table. That is, OFS communicates directly without passing through OFC. According to OpenFlow, it is possible to flexibly carry out network control such as path control and load balance on the basis of OFC's setting the flow which is applied to OFS.
That is, the OpenFlow protocol determines the flow with reference to contents of the packet which exist in L1 to L4. For example, according to OpenFlow, OFS transfers fields (Match Field) of L1 to L4 of a communication packet to OFC by using the Packet-in (P-in) message. Then, OFC inputs a determined flow into OFS. On the basis of the above-mentioned operation, OpenFlow realizes the flexible network control, for example, network control of carrying out the adequate path control and distributing network traffic.